On January 1, 1967, the entire membership (17,800) of the Asbestos Workers' Union (insulation workers) in the United States was registered. Much information was obtained, including smoking habits. Each worker has been kept under observation since. For the period through December 31, 1971, l,092 men died and causes of death have been ascertained. We will maintain prospective observation of this well-defined cohort. Information will be obtained on the following problems: lung cancer deaths among non-smoking asbestos workers (to determine whether asbestos alone, without cigarette smoking, increases the risk of bronchogenic carcinoma); the relationship of cigarette smoking to pleural and peritoneal mesothelioma; its relation to pulmonary fibrosis (current observations are of borderline statistical significance and further data are needed); interaction between smoking and gastrointestinal neoplasms; relationship of cigarette smoking to other neoplasms among asbestos workers. We will further be able to ascertain whether cessation of cigarette smoking will decrease the risk of lung cancer among asbestos workers, information of potentially great value in their management and surveillance. The design of the investigation will also allow accumulation of data bearing on special risks of shipyard insulation work, effect of variations in age and time of onset of exposure, and of lapsed period from onset of exposure. BIBLIOGRAPHIC REFERENCES: Hammond, E. C., Selikoff, I. J. and Seidman, H. Multiple interaction effects of cigarette smoking: Extrapulmonar cancer. In: Proc. XI Int. Cancer Congress, Florence, 1974, Cancer Epidemiology, Environmental Factors, Vol. 3. Ed. Pietro Bucalossi, Umberto Veronesis and Natale Cascinelli. Excerpta Medica, Amsterdam and American Elsevier Publishing Company, Inc., New York, 1965. pp. 147-150.